Optical system with bright light output

ABSTRACT

An optical system producing bright light output for optical pumping, communications, illumination and the like in which one or more fiberoptic waveguides receive light from one or more diode lasers or diode laser bars and transmit the light to an output end where it is focused or collimated into a bright light image. The input end of the fiberoptic waveguides may be squashed into an elongated cross section so as to guide light emitted from an elongated light source such as a diode laser bar. The waveguides are preferably arranged at the output end into a tightly packed bundle where a lens or other optical means focuses or collimates the light. For diode laser bars much wider than 100 microns, a plurality of waveguides may be arranged in a line to receive the light, and then stacked at the output in a less elongated configuration. In this manner, light from many diode lasers or laser bars may be coupled through the bundle into the end of solid state laser medium.

This is a divisional of co-pending application Ser. No. 43,612 filed onApr. 28, 1987 now U.S. Pat. No. 4,763,975.

TECHNICAL FIELD

The present invention relates to optical systems for producing a brightlight output, and in particular to fiberoptic systems having a laserlight source.

BACKGROUND ART

Many different methods are available for pumping solid state lasers,such as neodymium doped yttrium aluminum garnet (Nd:YAG) lasers. Onecommon technique is to place a rod of solid state material at one focusof a tubular reflector having an elliptical cross section and a flashlamp or other bright light source at the other focus. In such anarrangement, light emitted by the flash lamp and reflected from thereflector walls will impinge on the rod. One problem with thisarrangement is that the rod must have a diameter large enough to absorba substantial portion of the pumping radiation during passage throughthe rod. If during this initial traverse the pumping illumination is notabsorbed, it is likely to be reflected by the reflector walls back tothe light source, where it will be reabsorbed, generating heat andreducing the lifetime of the source. Another problem is that much of theoptical energy produced by flash lamps and other broadband light sourcesis wasted, because it does not match the absorption spectrum of thelaser medium.

In U.S. Pat. No. 3,982,201, Rosenkrantz et al. disclose a solid statelaser in which a Nd: YAG laser rod is end pumped by an array ofsemiconductor laser sources. The wavelength of the pump light from thediode lasers is selected for optimum absorption, while the increasedoptical path length of the pump light within the rod from end pumpingrelative to that from side pumping ensures more complete absorption. Thelasers are cryogenically cooled and operate in a pulsed mode with a lowduty cycle to enable heat generated by the diodes to dissipate betweenpulses and thereby maintain the array at a temperature which providesthe desired pump wavelength.

Individual diodes and diode lasers, as well as arrays of diode lasersjust described, have been directly coupled to the end of solid staterods to achieve low to medium power laser output. However, the poweroutputs of these solid state lasers are limited by the brightness of thepump light. In order to achieve higher power, brighter pump sources arerequired along with efficient means for coupling light from thesesources into the solid state medium.

In U.S. Pat. No. 4,575,854, Martin discloses a Nd:YAG laser which isside pumped by a plurality of diode laser bars. Each bar contains manydiode lasers which in turn circumferentially envelope a Nd:YAG rod orother suitable solid state medium. The bars are driven by a highfrequency pulse which is switched so as to drive the bars in any desiredcombination, but not all at the same time. The laser operates in acontinuous wave mode even though any given laser bar is pulsed at a verylow duty factor so that the array may operate uncooled.

Diode laser bars with 30 W peak power output, a 50 Hz repeat rate and a150 μsec pulse length have been demonstrated, and it would be desirableto use laser bars to end pump a solid state laser. However, if one weresimply to butt couple a diode laser bar to the end of a solid state rod,the laser would not be efficiently pumped, because of the elongateddiode laser bar geometry. Laser bars may have a lateral dimension orwidth of up to 1 cm, which is too great to form a small enough image tofit within the fundamental mode volume of a solid state rod. Typicalrods are 3 mm in diameter and have a fundamental mode volume about 100μm in diameter.

In U.S. Pat. No. 4,653,056, Baer et al. disclose an intra-cavityfrequency-doubled Nd:YAG laser which allows efficient coupling by a highpower laser diode array, despite the fact that the diode array has anoutput beam with too much spatial structure and limited focusability.Baer et al. achieve this result by expanding the lasing volume to matchthe focused image of the laser diode array. A combination of a concaveoutput coupler mirror and a lens-shaped end at the front end of theNd:YAG rod enables the beam size within the YAG rod to be adjusted tothe appropriate volume. For efficient pumping, the pumping volume mustoverlap and preferably match closely the lasing volume of the rod.

It is not always possible or desirable to change the shape and size ofthe mode volume to match the pump light of a diode laser bar. Further,it may be desired to further increase the power by using a plurality ofdiode laser bars for pumping, as taught for example by Martin. Thus,ways of producing a bright source that fits the available mode volume ofa solid state laser are sought. It may also be desired to operate aplurality of diode laser bars continuously, but still provide thenecessary heat dissipation.

An object of the present invention is to produce an optical pumpingsystem for end pumping a solid state laser.

DISCLOSURE OF THE INVENTION

The above objects have been met with optical pumping systems in whichone or more fiberoptic waveguides receive light from one or more diodelasers or diode laser bars and transmit the light to an output end whereit is formed into a bright light image and coupled into an end of asolid state active medium. The input end of a fiberoptic waveguide,which in the prior art is typically round with a diameter substantiallyequal to that at the output end, has in the present invention elongatedcore dimensions and lateral and transverse numerical aperturescorresponding respectively to the typically elongated emissive area andto the lateral and transverse divergences of the light source to whichit is coupled, so as to guide most of the light emitted by that source.In other words, the fiber may be squashed, flattened or otherwiseelongated at the input end to match the light output by the diode laseror diode laser bar, and may be tapered to a smaller core area at theoutput end to match the solid state rod or slab. The optical poweremitted at the output end of a fiber waveguide is greater than 50% ofthe total diode laser power output, and waveguide outputs as high as 88%of total laser output have been demonstrated. However, because the lightemitted at the output end of an elongated fiber has a higher powerdensity than that obtained by butt coupling a laser array to a circularcore fiber of the same diameter as the laser array, the overall pumpingefficiency is improved. Further, because the fiber coupled laser diodecan be remotely located, thermal dissipation in the region of a solidstate laser medium is not a problem.

Focusing optics proximate the output end may be used to image the lightinto a very bright spot forward of the end of the bundle, or into acollimated beam. Alternatively, butt coupling as an input to anotherdevice may be used. An input end of a fiber waveguide is positionedproximate to a light source for accepting light therefrom. A lens orother optical means may then couple the light into the cavity modevolume of a solid state laser medium if desired.

The present invention solves the problem of coupling elongated lightsources, such as diode laser bars, into the mode volume of a solid statelaser. The invention also produces a bright light source, especiallywhere light divergence precludes lenses and where spacing and thermaldissipation problems preclude use of multiple sources. Using fiberopticwaveguides, the problem of increasing brightness is separated fromusually related problems of spacing and heat dissipation. In addition tobeing used to optically pump solid state lasers, the optical system ofthe present invention, producing bright light output, may be used forsurgery, scribing, welding, cutting, illuminator systems, such asbeacons, communications links, rangefinders and the like.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified side view of an optical system of the presentinvention with a solid state laser.

FIG. 2 is a perspective view of a laser light source and the input endof a fiberoptic waveguide in the optical system of FIG. 1.

FIG. 3 is a front end view of a fiberoptic bundle of the optical systemof FIG. 1.

FIG. 4 is a side plan view of the fiberoptic bundle in FIG. 3 buttcoupled to an end of a solid state laser medium.

FIG. 5 is a side plan view of a second optical system and solid statelaser embodiment of the present invention.

FIG. 6 is a side plan view of a third optical system and solid statelaser embodiment of the present invention.

FIG. 7 is a side plan view of a fourth optical system and solid statelaser embodiment of the present invention.

FIG. 8 is a perspective view of a diode laser bar and a plurality offiberoptic waveguides for another optical system of the presentinvention.

FIG. 9 is an end view of the diode laser bar of FIG. 8 taken along theline 9--9.

FIG. 10 is an end view of the stacked output end of the fiberopticwaveguides of FIG. 8.

FIG. 11 is a perspective view of the output end of FIG. 10 coupling to asolid state laser slab.

FIGS. 12-16 are side perspective views of embodiments of the output endof a fiberoptic waveguide bundle in accord with the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, an optical system for producing a bright lightoutput useful for pumping a solid state laser includes a plurality ofsemiconductor laser light sources, such as diode lasers or diode laserbars 11, 12 and 13. Typically, there are seven laser light sources,although the number may vary. Each of the laser light sources 11, 12 and13 emits a light beam 25 which couples into one of a plurality offiberoptic waveguides, such as waveguides 17, 18 and 19. The waveguides17, 18 and 19 are arranged to form a bundle 23, and emit the light 25guided by waveguides 17, 18 and 19 from light sources 11, 12 and 13 andemitted at an output end 27 of the waveguide bundle 23. Optics, such asthe lens of lens system 29 in FIG. 1, may be disposed in front of outputend 27 to focus the light 25 into a bright light image which may, forexample, couple into the end 31 of a solid state laser medium 33.Alternatively, the fiber bundle may be butt coupled to the rod. Notethat the solid state laser rod may act as a light guide via totalinternal reflection in order to confine the diverging pump light rays,thereby allowing for more efficient light absorption.

Each light source 11, 12 and 13 is typically a high power semiconductordiode laser bar, such as any of the (GaA1)As phased array lasers orbroad area lasers known in the art. Alternatively, semiconductor diodesand individual diode lasers may be used. Lasers and laser arrayscomposed of light emitting semiconductor materials other than (GaA1)As,such as InGaAsP, may also be used. Typically, each light source emitswith a continuous wave optical power output of at least 200 mW, andpreferably at least 500 mW. Semiconductor laser arrays with facetwindows fabricated by silicon impurity induced disordering have beendemonstrated with continuous power outputs of up to 3 Watts beforeexhibiting catastrophic facet damage. One such laser is disclosed in anarticle by R. L. Thornton, et al. in Applied Physics Letters, vol. 49,no. 23, Dec. 8, 1986, pp. 1572-1574. In short pulse operation, i.e.shorter than 1 μs pulse lengths, the catastrophic power limit increasesinversely as the square root of the pulse length. Lasers with 100 nsecpulses and 10 kHz repeat rate can be used in the present invention toproduce an optical system with 20 W peak power output from the fiberbundle 23. The lasers can be modulated up to gigahertz rates by simplyvarying the drive current so that the system can be used as part of acommunications link.

A power supply 35, in electrical communication with laser light sources11, 12 and 13, as indicated by arrow 37, supplies electrical power todrive the light sources. Typically, the light sources operate at about25% electrical to optical overall efficiency. Efficiencies of up to 50%have been achieved. Accordingly, each laser light source producing 500mW continuous optical power output draws about 1 A current at 2 V. Thus,power supply 35 may be a lightweight portable battery unit delivering atleast 14 W. The light sources 11, 12 and 13 may be connected in any ofvarious series-parallel combinations depending on the most convenientpower supply. The remaining electrical power drawn by the light sourceresults in heat which is removed by heat sinks 39, 40 and 41.Temperature control may be required in some optical pumping applicationsto ensure that the wavelength of the laser output coincides with theabsorption band of lasing material 33. The system typically operates atthe ambient temperature, i.e. about 15° C. to 25° C.

With reference to FIG. 2, each laser light source 11 has an elongatedemissive area. For example, the preferred diode laser bar 11, seen inFIG. 2 typically has a substantially rectangular emissive area with alateral dimension or width of about 100 μm and a transverse dimension orheight of about 1 μm. The far field profile of the emitted light 45 fromsuch a laser is characterized by lateral and transverse divergences,typically about 7° and 30° respectively.

In order to efficiently couple light 45 from laser bar 11 into afiberoptic waveguide 17, the waveguide is squashed at one end into anelongated shape. Waveguide 17 comprises a transparent core 47characterized by a first index of refraction, and a cladding 49surrounding core 47 and characterized by a second lower index ofrefraction. The cladding 49 is preferably thin, i.e. about 2 μm thick.The numerical aperture (N.A.) of a fiberoptic waveguide, i.e. the sineof the half-angle within which the fiber can accept or radiate lightguided by the fiber, is a function of the indices of refraction of core47 and cladding 49 and other factors, and is indicative of the abilityof the fiber or waveguide to couple light from laser light sources 11,12 and 13. Typically waveguide 17 is an 0.3 N.A. waveguide with a 50 μmcore diameter circular cross section, which is then elongated at aninput end 51 to an elliptical cross section with 120 μm by 20 μm coredimensions. Transition from circular to elliptical cross section isabout 0.5 cm but the fiber could be several meters in length. Squashingthe fiber waveguide causes the core material to emerge slightly from thecladding in the form of a semi-ellipsoidal lens. This lens may beretained to further improve coupling into the fiberoptic waveguide 17 orthe waveguide end 51 may be mechanically polished flat for butt couplingto laser bar 11. Fiberoptic waveguides with rectangular cross sectionsmay also be used.

The fiberoptic waveguide 17 is shown in FIG. 2 to be spaced proximate tolaser bar 11. Typically, however, waveguide 17 abuts laser bar 11 withthe major elliptical axis of the waveguide core aligned with the lateraldirection of laser bar 11. The waveguide 17 efficiently couples lightfrom laser bar 11 because the elongated core dimensions correspondclosely to the dimensions of the laser bar's emissive area. Further, theinput numerical apertures measured in both the lateral and transversedirections are altered by the flattening process from the intrinsicnumerical aperture of the circular core fiberoptic waveguide from whichwaveguide 17 is formed. Typically, waveguide 17 has a lateral numericalaperture of about 0.125, corresponding to acceptance of light with up to14° lateral divergence. Waveguide 17 also has a transverse numericalaperture of about 0.75, corresponding to acceptance of light with up to97° transverse divergence. These acceptance angles are at least twicethe lateral and transverse divergences of the laser bar 11, sufficientto couple most of the light emitted by laser bar 11. Typically, thecoupling efficiency is at least 50% and typically about 75%. Couplingefficiencies as high as 88% have been achieved.

With reference to FIG. 3, the plurality of fiberoptic waveguides 17, 18and 19 in FIG. 1, are arranged into a bundle 23 of waveguides, hereindicated by the reference numerals 55a through 55g. Typically, thewaveguides 55a-55h are arranged in a hexagonal close packed array formaximum brightness. Seven waveguides, having core diameters of about 50μm and cladding thicknesses of about 2 μm, produce a bright light sourcewith an effective diameter D of about 170 μm. For lasers with 500 mWcontinuous output, and a 75% coupling efficiency, the bundle 23 producesa continuous bright output of approximately 2.5 watts. Higher poweroutputs up to about 7.5 watts continuous wave can be achieved if theindividual lasers operate up to their catastrophic limits, orsequentially in a pulsed mode.

With reference to FIG. 4, an output end 27 of a bundle 23 of fiberopticwaveguides is butt coupled to an end 31 of a solid state active lasingmedium 33. The medium 33 may be in the form of a cylindrical rod, asshown, or a rectangular slab or other convenient shape. The medium 33may be any solid material which has been developed for lasers, includingneodymium doped yttrium aluminum garnet (Nd:YAG), Nd:glass, Nd:YLF,Nd:YALO, Er:YAG, ruby, and alexandrite, provided the output wavelengthof the fiberoptic bundle 23 matches an absorption band of the medium 33.For example, for Nd:YAG pumping, the light 25 output by laser lightsources 11, 12 and 13 and transmitted by fiberoptic bundle 23 has awavelength of about 0.8 μm. End 31 of medium 33 typically has a coatingwhich is highly reflective at the lasing wavelength, 1.06 μm for Nd:YAGlasers, and which is antireflective and highly transmissive to light 25at the pumping wavelength, 0.8 μm for Nd:YAG lasers. Butt coupling, asseen in FIG. 4, is adequate for multimode laser operation, but may wasteconsiderable optical energy for single transverse mode laser operation.

Referring again to FIG. 1, in order to efficiently pump medium 33 forsingle transverse mode operation, it is preferable that the pump light25 emitted from bundle 23 be focussed to a spot size which substantiallymatches the mode volume of the desired lasing mode. This mode volume isdetermined from the resonant optical cavity of the solid state laserdefined between end 31 and laser output mirror 57. The mode volume 59 inactive medium 33 is a function of the curvatures of end 31 and mirror 57and the distance between them. Typically, for a 3 mm diameter rod, thelowest order mode volume has a diameter of about 100 μm. A lens 29 ormultiple lens system may be used to focus the light from bundle 23.Typically, lens 25 has a focal length of about 6 cm.

Applications other than optically pumping a solid state laser, such ascommunications, illumination, beacons and the like, require a collimatedbeam output from bundle 23. To produce a beam divergence comparable to a1 to 10 mW helium-neon laser, i.e. a 1 mrad divergence, a 17 cm focallength lens 29 is required. Lens 29 should have a diameter of about 10cm for a bundle of 0.3 N.A. fiberoptic waveguides. Such a systemproduces an optical power density of about 0.35 μW/cm² at a distance of30 km, which is easily detectable by conventional siliconphotodetectors.

With reference to FIGS. 5-7, an optical pumping system for pumping asolid state laser includes a semiconductor diode laser bar 61, broadarea laser or other elongated light source. Laser bar 61 emits a lightbeam 62 which is coupled into a fiber optic waveguide 63. The input endof waveguide 63 is elongated, as in FIG. 2, so as to have coredimensions and lateral and transverse numerical apertures whichcorrespond respectively to the emission area and lateral and transversedivergences of laser bar 61. Thus, waveguide 63 butt coupled orotherwise positioned proximate to laser bar 61 guides most of the light62 emitted by laser bar 61. Various optical means are shown for couplinglight 64 emitted from the output end of waveguide 63 into an end 66 ofsolid state laser material 67. In FIG. 5, a focusing lens 65 coupleslight 64 into medium 67. In FIG. 6, waveguide 63 is butt coupled to theend 66 of medium 67. In FIG. 7, one or both of end 75 of waveguide 63 orsurface 77 of end 66 is curved, thereby effectively focusing light 64into medium 67. These optical means cooperate with the output end ofwaveguide 63 to match the light 64 to a desired mode of the resonantoptical cavity of the laser. Solid state medium 67 may be in the form ofa cylindrical rod, rectangular slab or other convenient shape.Reflective output mirror 69 may have a concave surface 73 or be planar.Medium 67 is typically provided with a coating on end 66 which is highlyreflective at the lasing wavelength and antireflective at the pumpwavelength. With any of these embodiments, the light from the elongatedemissive area of a diode laser bar is efficiently coupled into the modevolume of a solid state laser.

With reference to FIG. 8, a semiconductor diode laser bar 81 may have awidth greater than 100 μm up to 1 centimeter or more. The laser bar 81may thus emit a plurality of light elements ranging from a few toseveral thousand or more. To date, 100 μm core diameter fibers have beensquashed to 460 μm by 18 μm cross sections with a coupling efficiencygreater than 50 percent. It may be somewhat difficult to squash a singlefiber to dimensions of 1 cm width.

In FIG. 9, laser bar 81 comprises a plurality of contiguoussemiconductor layers 83, 85, 87, 89, 91 and 93, of which at least onelayer 87 forms an active region for lightwave generation and propagationunder lasing conditions. Laser bar 81 may be constructed in any of theknown ways for producing a laser bar 81, preferably with stable phaselocked output. For example, laser bar 81 may have a plurality ofconductive contact stripes 95 for introducing lateral gain guiding.Laser arrays with real refractive index guiding may also be used. Activeregion 91 together with cladding layers 85 and 89 form an emissive areaat reflective facet 97, emitting light elements 99, seen in both FIG. 8and FIG. 9.

For the purpose of coupling this emissive area to fiberoptic waveguides,the emissive area formed by layers 85, 87 and 89 is divided into aplurality of segments demarcated by dashed lines 101. The divisions maybe made anywhere in the emissive area, provided that each segment emitsat least one light element 99 in the array of light elements, andprovided that the width of each segment does not exceed 200 μm at mostand preferably does not exceed 150 μm. In FIG. 8, a plurality offiberoptic waveguides 103, 105, 107, etc. are disposed in front of theemissive area of laser bar 81 for accepting and guiding light elements99 from the laser segments. Preferably, the core of each waveguide 103,105, 107, etc. has a rectangular cross section, although elliptical andcircular cross-section waveguides may also be used. The input end ofeach waveguide has squashed or elongated core dimensions correspondingto the dimensions of the laser segment proximate thereto, and shouldalso have lateral and transverse numerical apertures corresponding torespective lateral and transverse divergences characteristic of thelasing elements 99.

Referring to FIGS. 10 and 11, the fiberoptic waveguides 103, 105, 107,etc. are stacked or otherwise arranged at an output end 109 to form abundle with less elongated dimensions than the laser bar's emissivearea. This bundle may be coupled to an end of a solid state laser medium110, here shown as a rectangular slab. For example, if laser bar 81 hasan emission area 1 mm wide and 10 μm high emitting 100 light elements,the emissive area may be divided into 10 laser segments each 100 m wideand each containing 10 light elements. Each fiberoptic waveguide 103,105, 107, etc. may then be elongated at the input end to 100 μm wide by20 μm high with core dimensions of about 96 μm wide and 16 μm high. Whenstacked or arranged into a bundle at the output end as shown in FIG. 10,the bundle measures 100 μm wide by 200 μm high. The elongation of thelight emitted by laser bar 81 has thus been reduced in this example froma width to height ratio of 100 to 1 to a ratio of 2 to 1. Otherdimensions and other stacking configurations may be used to produce aless elongated light output for optical pumping or other application.

In FIGS. 12-16, various ways of forming the output end of a fiber bundle111 are seen. In FIG. 12, the end of bundle 111 is fused so as to form abead 113 of molten core material. When the bead 113 cools and hardens,all of the fiber waveguides of bundle 111 are fused together. Further,the surface 115 of bead 113 is curved so as to function as a convergentlens to light output from the waveguide bundle. In FIG. 13, a greaterlength of bundle 111 is heated, preferably to the melting point of thefibers. As a result, the fibers are not only fused together, but alsoair gaps, such as gaps 117 in FIG. 4, between the fibers are removed anda homogeneous rod 119 is formed on the end of bundle 111. Rod 119functions as a mixing rod to blend the light coming from the individualfiber waveguides of bundle 111 and thereby produce a more spatiallyuniform light output. Further, because the air gaps have been removed informing rod 119, the rod 119 has a reduced diameter and greater opticalpower density than bundles without this rod. The original diameter ofbundle 111 is indicated by dashed lines 121 representing the originalfiber waveguides from which rod 119 was formed. In FIG. 14, the fiberbundle 111 is further processed by a combination of heating and pulling.A tapered output rod 123 results. Tapered rod 123 is characterized by adiameter which is typically reduced by about one-half compared to mixingrod 119 in FIG. 13. This produces a greater optical power density butalso with greater light divergence. For example, a 200 μm diameterbundle of 0.3 NA fibers, when terminated in a rod 123 tapered to 100 μmdiameter emits light with a 0.6 NA.

In FIGS. 15 and 16, the output end of fiber bundle 111 is not melted,but instead butted against a glass mixing rod 125. In FIG. 15, rod 125performs the same function as melted rod 119 in FIG. 13, namely blendingthe light from the fiber waveguides of the bundle to produce a uniformlight output. If desired, an antireflection coating may be applied tothe end 126 of rod 125. In FIG. 16, a partial reflector 127 is added tothe end of rod 125. Portions of the light rays 129 diverging from fiberwaveguides in bundle 111 is reflected by mirror 127 back into the bundle111. This light is then coupled back into laser light sources on theinput ends of the fiber waveguides. Since the light diverges and ismixed in rod 125, a portion of the light originating from one laser endsup being coupled back into another laser, and the lasers can becomephase locked. Thus, the embodiment in FIG. 16 produces coherent emissionfrom all the lasers in the bundle. Preferably, the fiberoptic waveguidesare polarization preserving single mode fibers. A reflectivity of atleast 5% for mirror 127 is sufficient to produce coherent light output.

The present invention produces a bright light output derived from aplurality of light sources or an extremely elongated light sourcesuitable for optical pumping a solid state laser. The invention is alsoapplicable as a communications link for ground-to-ground, ground-to-air,ground-to-space, ship-to-shore communications, as a designator, rangefinder, illuminator, beacon, welding, cutting, scribing, or any otherapplication requiring a bright collimated light source.

We claim:
 1. An optical pumping system for a solid state lasercomprising,light source means for optically pumping a solid state activemedium in a resonant optical cavity, said light source means emittinglight from an elongated emissive area with given lateral and transversedivergences, a fiberoptic waveguide having an input end and an outputend, said input end positioned relative to said light source means foraccepting light emitted therefrom, said input end having oblong coredimensions and lateral and transverse numerical apertures correspondingrespectively to said emissive area and said lateral and transversedivergences so as to guide most of said light emitted by said lightsource means, and optical means in proximity to said output end of saidwaveguide for coupling said light into an end of said solid state activemedium, said output end and said optical means cooperating to match saidlight to a desired mode of said resonant optical cavity.
 2. The systemof claim 1 wherein said light source means is a broad area diode laser.3. The system of claim 1 wherein said light source means is a laserdiode bar, said waveguide having an input end with an oblong core with awidth at least as great as that of said laser diode bar.
 4. The systemof claim 1 wherein said light source means operates in a pulsed mode. 5.The system of claim 1 wherein said light source means operates in acontinuous mode.
 6. The system of claim 1 wherein said medium is in theform of a cylindrical rod.
 7. The system of claim 1 wherein said mediumis in the form of a rectangular slab.
 8. The system of claim 1 whereinsaid optical means is a focusing lens between said output end of saidwaveguide and said end of said medium.
 9. The system of claim 1 whereinsaid optical means is a curved surface on at least one of said outputend of said waveguide and said end of said medium.
 10. The system ofclaim 1 wherein said optical means is butt coupling said output end ofsaid waveguide to an end of said medium, the end having a coating whichis transmissive to light from said light source means but highlyreflective to laser light wavelengths of said medium.